Garden Variety: Tougher poison ivy

If you have ever had a reaction to the plant, just the inscribed memory of endless itching might make you doubtful that anything could rival it. For gardeners and outdoor enthusiasts who regularly encounter poison ivy, however, the rumors that the plant is becoming more abundant are starting to look true.

The news about poison ivy (Toxicodendron taxa) is more than rumor, but if you heard it from a friend, it would be easy to put it in a box with old wives’ tales and snake oils. Research at Duke University in the early 2000s started the discussion when the results of a six-year study on the relationship between poison ivy and elevated atmospheric carbon dioxide were released.

The bottom line from the report’s abstract reads: “Our results indicate that Toxicodendron taxa will become more abundant and more ‘toxic’ in the future, potentially affecting global forest dynamics and human health.”

In the study, when atmospheric carbon dioxide increased in a forest, poison ivy was able to photosynthesize better and use water more efficiently, making it grow faster and larger than it would otherwise. In addition, the urushiol (the oil responsible for skin irritation) produced by these plants was more allergenic than in plants at normal atmospheric carbon dioxide levels.

Elevated atmospheric carbon dioxide is related to growth stimulation in other species of plants also, but the rate of increase in poison ivy is higher than most and will help the plant outcompete others as carbon dioxide levels increase.

Unfortunately, little can be done to stop poison ivy besides avoidance and controlling it on your own property. Learn to recognize the plant, characterized by compound leaves with three leaflets. Poison ivy can be a vine, a shrub or something that looks like a perennial groundcover with single leaves coming out of the ground. Along the Kansas River north of Lawrence, large patches of waist-high poison ivy are easy to find. By mid-to-late summer the leaves often have reddish spots on them that make them easier to recognize.

If you encounter poison ivy, avoid touching any part of the plant or contacting it with tools or clothing. Urushiol, the oil produced by the plant, can be carried on objects and cause a reaction later through indirect contact. Urushiol can also be inhaled if poison ivy plants are burned.

According to the Centers for Disease Control and Prevention, 80 to 90 percent of humans are allergic to urushiol, but allergies can develop for those who think they are immune. Urushiol reactions are characterized by itchy red bumps, patches and weeping blisters.

— Jennifer Smith is a former horticulture extension agent for K-State Research and Extension and horticulturist for Lawrence Parks and Recreation. She is the host of “The Garden Show” and has been a gardener since childhood. Send your gardening questions and feedback to Lawrence Living@ljworld.com.